Write a function that accepts an input that is a single integer score and outputs the corresponding letter grade according to the following grading scale: Score values ranging from 90 to 100 receive an A. Score values ranging from 80 to 89 receive a B. Score values ranging from 70 to 79 receive a C. Score values ranging from 60 to 69 receive a D. Score values ranging from 0 to 59 receive an F. #FUNC, #CHAR